Hydraulic control mechanism



A ril 24, 1934. J. 1.. CLOUDSLEY 1,956,117

HYDRAULIC CONTROL MECHANISM Filed April 25, less 4 Sheets-Sheet 1 April 24, 1934. J CLOUDSLEY 1,956,117

HYDRAULIC CONTROL MECHANISM Filed April 25. 1933 4 Sheets-Sheet 2 INVENTOR in War TTORNEY April 1934- J. L. CLOUDSLEY 1,956,117

HYDRAULI C CONTROL MECHANI SM Filed April 25. 1935 4 Sheets-Sheet 3 28 0 'I5 33 I -25 1 29 52 n L. o \J/ Fig. 3. 5 21 fr. mi

Arm/W5) April 1934. J. L. CLOUDSLEY 1,956,117

HYDRAULIC CONTROL MECHANISM Filed April 25, 1933 4 Sheets-Sheet 4 Patented Apr. 24-, 1934 TES FFl fiE TENT Application April 25, 1933, Serial No. 667,912 in Great Britain April 28, 1932 14 Claims.

This invention relates to hydraulic control mechanism and has particular reference to the positioning of a control piston in a cylinder by causing hydraulic pressure to act upon the piston in opposition to a spring or other form of reaction member. If an outlet port is provided close to the flu d inlet to the cylinder and above the face of the piston when the latter is in its initial position so as to serve as a. permanent leak, the stage at which the piston will commence to move in response to increasing inflow pressure of fluid will depend on the size of the leak or the setting of a cook or valve therein. If on the other hand the port is located at some appreciable distance down the wall of the cylinder, the piston will commence to move immediately the entering oil overcomes the reaction force on the piston and will continue to move until it uncovers the port, and if a steady fluid pressure is maintained by circulation of the fluid as for example by means of a gear pump the piston will take up a position determined by the posit-on of the port in the wall of the cylinder.

The movements of the piston as just described can be usefully applied for a variety of purposes for example for the actuation of a relay, a valve, a clutch, a rheostat arm or a brake band lever. A particularly useful application is in variable speed power transmission mechanism for motor veh'cles in which case the position of the piston may determine the gear ratio; for example as the piston recedes it may change the speed ratio progressively from bottom gear to top gear or vice versa.

The chief object of present invention is to increase the functional capabilities of hydraulic control mechanism of the above stated kind and with this object in view the invention in its broad aspect consists in render'ng the side port for the pressure fluid isplaceable along the cylinder or in providing a particular form of leak port control as he "einafter described or in utilizing these two methods of control in conjunction with one another.

A simple method for the purpose of altering the position of uncovering of the side port is to employ a sleeve axially movable with respect to the piston so that by shifting said sleeve the stage at which the port becomes uncovered is correspond'ngly altered.

The present invention functions very effectively in hydrauli ally operated infinitely variable gear control mechanism in which the fluid under pressure. such as that derived from an oil pump driven from the eng'ne under control, can escape not only through the above-mentioned side port when uncovered by the piston but can also escape,

ti'ircugh a leak port as above mentioned, the leak ng of predetermined bore and having an .obturator by which the capacity of the p1pe can be regulated. Variations in the degree of obstruc tion experienced in the leak pipe cause Variations in the engine speed at which positions of equilibrium will be assumed by the piston up to the position at which the latter uncovers the side port, beyond wh'ch no further rise in gear ratio can take place unless the position of the side port itself be altered. In such a case it will be understood that the capability of shifting the side port in accordance with the present invention is equivalent to ability to change the upper limit of gear ratio.

A further feature of the present invention consists in linking up the sleeve adjusting mechanism with the main transmission lever of variable speed power transmission mechanism in such a way that when and so long as this lever is in the neutral or uncoupled position or in the position of reverse drive the sleeve remains in the position which prevents the control piston from forcing the variable speed power transmission mechanism into a high gear ratio position. A similar linkage may also be applied to the valve or cook of the leak port or a separate leak valve may be provided solely for operation by such linkage.

In order that the invention may be clearly understood and readily carried into effect, I will now describe the same more fully with reference to the accompanying drawings in which:-

Figures 1, la, 11), 1c and 1d are longitudinal sections showing in difierent positions a portion of hydraulic control mechanism in accordance with the invention. Figure 1c is a sectional View of a control piston and plain cylinder with only a leak passage and valve.

Figure 2 is a longitudinal section of a modified form of the mechanism shown in Figure 1 and illustrating it attached to one end of the casing of a variable speed power transmission gear.

Figure 3 is a sectional end elevation of the mechanism shown in Figure 2, and Figure 4 is a corresponding sectional plan View, both of these figures also showing means for actuating the sleeve associated with the control piston.

Figure 5 is a section on the line 5-5 of Figure 3.

Figures 6, 7 and 8 are detail views of mechanism for actuating the leak valve.

Referring first to Figures 1, 1a, 1b, 1c and 1d, it is seen that the hydraulic control mechanism illustrated comprises a cylinder 1 having an oil inlet 2, a permanent oil outlet or leak port 3, and a second oil outlet or side port 4. Within the cylinder 1 is a sleeve 5 axially adjustable by means of a connecting rod 6 and having a port 7 which registers with the elongated port 4 in the cylinder.

Within the sleeve 5 is the piston 8 which is normally thrust towards the oil inlet 2 by a spring 9. The piston has a rod 10 by means of which it exerts its operating or controlling force on some device, such as a relay, valve, clutch, brake band or change speed control lever. Leakage from the pipe 3 is controlled by a cook or valve 11.

For convenience of further description I will suppose that the piston operates through the piston rod 10 to control an infinitely variable speed power transmission mechanism of the kind in which a torque reaction occurs which will assist the spring 9. The uppermost position of the piston corresponds to bottom gear ratio in the transmission mechanism. Depression of the piston raises the gear ratio.

Assume, as is the general case in practice, that the oil is being constantly forced into the cylinder by an oil pump driven from the first motion shaft of the transmission mechanism and constantly escapes from the cylinder.

Consider first the parts in the position shown in Figure 1 and assume that the leak valve 11 is closed and that the port '7 is adequate to dischare the oil entering under pressure into cylinder 1. The piston will remain in bottom gear position, but by shifting the sleeve downwards to some selected position the port 7 will be temporarily covered as shown in Figure 1a and the piston will correspondingly descend to uncover the port as shown in Figure lb and will thereby cause a rise in gear ratio. The length of the port 4 is equal to the full stroke of the piston. Hence by shifting the sleeve 5 downwards any desired gear ratio can be established within the full range of the gear change mechanism. Evidently, therefore, ability to shift the sleeve amounts to ability to effect a servo-gear change. The sleeve may be shifted by manual control or by pedal control as hereinafter described.

Now consider the effect of the leak valve 11 and first assume that there is no sleeve 5 or port 4 as shown in Figure 1c. Since the oil pump is driven by the driving shaft of the transmission mechanism the oil pressure will vary with engine speed. The forces balancing the oil pressure are, of course, the pressure of spring 9 and the torque reaction. The pressure which any given engine speed will produce is dependent upon the setting of the leak valve 11. Assume some particular setting of the leak valve and a spring 9 of definite characteristics. In the case of the particular mechanism under consideration the torque reactive control member, namely the piston rod 10, carries from the transmission mechanism re actions which for any given input torque will vary with the gear ratio of the mechanism, and therefore the spring is so calibrated that the graph of its reaction supplemented by the torque reaction throughout the entire stroke of the piston is approximately a straight line. The control piston 8 will seek and settle in a position corresponding to the engine speed at which the prevailing torque reaction assisted by the spring 9 balances the oil pressure. Any momentary drop in torque reaction will cause a rise of engine speed which will cause increase of oil pressure r which will depress the piston against the reduced torque reaction and raise the gear ratio with the result that the torque on the engine is re-established, and therefore the rise of engine speed is counteracted. Conversely any momentary rise in torque reaction will lower the engine speed which will cause decrease of oil pressure which will cause the piston to rise assisted by the increased torque reaction and decrease the gear ratio sufficiently to reduce the torque and therefore allow the engine to restore its speed. The

tendency, therefore, is for the engine speed corresponding to some particular setting of the leak valve to be maintained constant automatically. Change of setting of the leak valve will cause a corresponding change in the definite engine speed. Now if the engine is running on full throttle at a certain speed its torque will be constant and so long as the torque reaction remains constant the control piston will remain stationary and no change in gear ratio will result. Assume this gear ratio to be a relatively high one as shown by the extent of depression of the piston in the figure (Fig. 16). If the torque reaction increases the control piston will become unbalanced and will move upwards from the position shown to a new position in which the gear ratio has become decreased to such a value as to enable the engine to maintain its speed. inversely, decrease of torque reaction willcause increase of gear ratio sufficient to load the engine and thereby induce it to maintain the engine speed. Therefore, any adjustment of the leakage at the valve 11 will change the engine speed which the gear will maintain. The practical advantage of adjustability of leakage at valve 11 is that for ordinary running conditions some nominal engine speed can be maintained and that for conditions under which high horse power is required the appropriate engine speed can be determined merely by adjustment of the leakage valve.

Now consider the eifects of both the leak valve and the sleeve and port 4 for which purpose take the conditions shown in Figure 1b and then partly open the leak valve as shown in Figure 1c. The first tendency is for the piston to rise and take up a position which will now be determined by the torque reaction, the spring pressure, and the pressure obtaining in the cylinder, and, in fact, the

piston will first rise slightly so that the position assumed by it will be one in which the leakage at valve 11 and the relief at port 7 are in parallel. Now assume an appreciable increase in torque reaction. The piston will be driven upwards thereby closing port '7 and will take up a position as shown in Figure 102 determined solely by the pressure in the cylinder which in turn is determined by the setting of the leak valve. The control of gear ratio is under these circumstances entirely automatic. Next, assume an appreciable decrease in torque reaction, the parts still being in the position shown in Figure 1d. The piston will immediately descend until it uncovers port 7 as shown in Figure 10 but will naturally descend no further and therefore the gear ratio will not be increased beyond the value corresponding to the position of these parts.

The general conclusions to be drawn from the foregoing are that the position of the port '7 as determined by adjustment of the sleeve 5 limits the degree to which the gear ratio can rise and that any upward movement of the piston due to increase of torque reaction will immediately establish the entirely automatic gear ratio control above described. This capacity to limit high gear ratio by adjustment of the sleeve 5 is of particular importance when driving in traiiic, be cause but for this capacity the light torque reaction consequent upon the partially throttled condition of the engine when travelling in traffic would tend to maintain inconveniently high gear ratio.

From the foregoing explanation of the diifer ent conditions and effects obtainable it will be realized that a valuable control can be efiected either by adjusting the leak valve 11 or by adjusting the sleeve 5 or by adjusting both.

I will now describe certain mechanical arrangements for adjusting both the leak valve and the sleeve in the modified construction illustrated in the remaining figures of the accompanying drawings.

In Figure 2 the cylinder 1 is shown as being mounted on the wall of the casing of a variable speed power transmission mechanism. The piston 8 is formed with a hollow cylindrical extension 12 within which slides the sleeve 5. The sleeve is shifted by a rod 6 secured by a bracket 13 to the lower end of the sleeve which in the position shown in Figure 2 just covers a port or ports 14 in the piston extension 12 of the piston 8. Oil from a sump in the casing of the transmission mechanism is forced by a gear pump 15 up the oil supply pipe 16 to a transverse oil passage 1'7. Part of the oil travels transversely (to the left in Figure 3) to and through a valve 19 on a stem 19a and along a passage 18 (Figures 4 and 5) and thence back to the sump, this being the permanent leak for the oil; another part of the oil travels transversely (to the right in Figure 3) to a passage 20 terminated in a springloaded excess pressure relief valve 21 past which escape takes place through a passage 2111 (Figure 4) to a space 34 hereinafter referred to; and the remaining oil passes straight on from pipe 16 into the top end of the cylinder 1. The oil from the top end of cylinder 1 passes down inside the sleeve 5 and past the spider or strap 13 to the bottom of the piston. It will therefore be understood that the oil pressure is acting upon the entire area of the piston but that the sleeve is in equilibrium as regards oil pressure.

Rise in oil pressure moves the piston against the resistance of the spring 9 and the prevailing torque reaction so that eventually the port 14 passes beyond the lower end of the sleeve whereupon the oil escapes through port 14 into the annular space 22 (Fig. 2) and thence out through a gap 23 in the cylinder 1 to the space 34. The lower end of the piston extension 12 is formed externally with an annular groove to receive the ends of a forked lever 24 by means of which the piston movements are converted into gear changing adjustments of the infinitely variable speed power transmission mechanism.

The oil constantly passing through the permanent leak valve 19 and the oil occasionally passing past the excess pressure relief valve 21 and also the oil passing through the port 14 in the extension 12 of the control piston 8 passes to a space 34 between the piston cylinder 1 and the adjacent rear wall 35 of the main gear casing and thence through a gap 36 in said wall and along an oil duct 37 to various bearings and other parts of the main gear for lubricating purposes, whence it finds its way to the sump from which it is again drawn by the gear pump for re-delivery to the control cylinder.

A relief valve 38 is provided on the duct 37 so that, in the event of undue obstruction in the bearings to circulation of the oil, the latter can escape through valve 38. This provision is important, as a substantial rise in pressure would interfere with the proper functioning of the hydraulic gear control unit.

As in the construction already described with reference to Figures 1, 1a, 1b, 1c and 1d, the stage at which the oil can escape past the port 14 in Figure 2 can be altered by shifting the sleeve relatively to the piston. In the position of the parts as shown in Figure 2 a slight downward movement of the piston will cause the port 14 to be uncovered and allow the oil to escape but by shifting the sleeve downwards the piston will need to descend a correspondingly great distance before causing the port 14 to become uncovered.

For the purpose of shifting the sleeve 5 its operating rod 6 is connected at its upper end to an arm 25 extending inside the head of the cylinder 1 from a shaft 26 (Figures 3 and 4) which pro jects at one end and has mounted thereon two arms 27 and 28, the short arm 2'7 being keyed to the shaft and the long arm 28 being loose thereon (Fig. 5).

The arm 27 is under the influence of a spring 29 and bears against a stop 30 on the arm 28 so that the tendency is for the arm 27 to follow the arm 28.

The extent of counter-clockwise movement of the arm 28 is limited by a stop piece 31 thereon coming against an adjustable stop 32. The extent to which the long arm 28 can rock to the right, i. e. clockwise, short of reaching the stop 33 can be regulated in any convenient manner. It will therefore be understood that the extent of downward movement of the sleeve 5, and hence the maximum gear ratio attainable by the transmis sion mechanism, is dependent upon the setting of the arm 28. This arm may be under the control of the foot of the operator or under his manual control, or both, as desired.

It has already been mentioned that the capacity of the permanent leak from the cylinder 1 determines the engine speed at which the critical oil pressure will be attained and act on the piston to enable it to move the latter toadjust the gear ratio to maintain such speed. In the arrangement shown in Figures 3, 4 and 5, the oil permanently leaks from the transverse passage 17 past the normally openpermanent leak valve 19 to passage 18 as already described. The oil es caping past the valve 19 traverses the passage 18 delivering into the space 34 between the cylinder 1 and the rear wall of the main gear casing and thence goes to lubrication as already described. The spindle of the valve 19 may be controlled by hand or foot or both through any suitable mechanism. For example as shown in Figure 6 the spindle of the valve 19 may have secured thereto an arm 44 carrying rotatably a pinion 45 which meshes with two gear sectors 46 and 47 mounted freely on the valve spindle. Gear sector 46 is rockable by hand (as for example by linkage to a hand lever on the steering column of the vehicle) and gear sector 47 is rockable by linkage to afoot pedal as shown in Figures 7 and 8. Thus for example the valve may be set by hand to any desired position and then the foot actuation may be superimposed.

The foot pedal 48 may be the actual accelerator pedal of the vehicle in which case the link 49 connecting it to the gear sector 47 has an clongated slot 50 therein as shown in Figure '7 so that depression of the pedal has no eifect on the permanent leak until the full acceleration position shown in dotted lines has been exceeded; alternatively the operating pedal may be a separate pedal 48a as shown in Figure 8 but preferably located close to the usual accelerator pedal 48 so that a driver can use one and the same foot to actuate both pedals. It is sometimes convenient to arrange both pedals side by side and so that they are level when the accelerator is fully depressed, against a stop 481) as shown in Figure 8, in which case the accelerator pedal will then steady the foot and act as a fulcrum or pivot on which the foot can rock to operate the second or leak pedal 48a.

Reverting to the means for actuating the spindle 26 of the sleeve operating arm 25 there may be provided, instead of or in addition to the manually settable arm 28, another arm 51 extending from the spindle 26 and connected by a link 52 to a pedal. fhe link operating pedal may be the usual accelerator pedal in which case the link 52 should be slotted as shown in Figure 3 so that the accelerator pedal is unable to actuate the arm 51 until it has passed its fully open throttle position; alternatively the pedal may be separate from the accelerator pedal but preferably near thereto similarly to the dual pedal arrangement already described with reference to Figures 6, '7 and 8.

With regard to mechanical linkage, either of the leak valve spindle or of the spindle of the sleeve operating arm to the accelerator pedal as above mentioned, it will be understood that control of the mechanism throughout the full range of the accelerator pedal movement can occur as usual quite unaffected by the linkage and that the effect of the linkage need only arise as the accelerator pedal is moved beyond the fully open throttle position. Al ough it has been assumed in the foregoing description of operation of the leak valve by a throttle-operating pedal that the valve is normally set and that it is operated by the pedal only when the throttle has been fully open, the operation can be otherwise. For example the leak valve can be normally closed when the throttle is closed and can open progressively as the throttle opens or can remain closed for a first stage of throttle opening and then progressively open during the later stage of throttle opening; also the shape of the leak valve or port may be such that it opens disproportionately to the opening of the throttle.

I will now refer to another problem that needs consideration when operating an infinitely variable power transmission mechanism in the manner and by the means hereinbefore described. As will be understood, when driving in reverse gear with a vehicle equipped as above described there is a tendency to increase the gear ratio whereas it is desirable during reverse travel to remain in low gear. Consider also the situation that arises if the engine fails for some reason at a moment when the variable speed gear is in topgear position. In such circumstances the vehicle will come to rest and the driver will instinctively put the main transmission lever into neutral and attempt to restart the engine and reestablish the transmission but he will find that the variable speed gear is still in the condition in which it existed when the engine failed, 1. e. in top-gear condition. If therefore the cause of engine failure has ceased to exist the driver will find that immediately the transmission is reconnected it may stall the engine.

In order to ensure that whenever the main transmission lever of the vehicle is put into neutral or reverse the setting of the above described sleeve is brought back to the position of mum gear ratio, a pin 39 on the short arm 27 engages an elongated slot ii) in a link 41 extending from said pin to a crank 42 on a shaft l3 operated by the main transmission lever. In the position shown in Figure 3 the crank i2 is in the position which it assumes during neutral or reverse in the main gear, and it is to be observed that the arm 27 cannot rock clockwise.

However, whenever the main transmission lever is moved out of reverse or neutral and into the forward transmission position the link 41 is driven to the right to the full extent of the slot 40 so that the arm 27 is free to follow any setting of the arm 28 quite free from any interference by the link.

In order that the leak valve spindle 19a as well as the sleeve 5 may be set and maintained in the position which will ensure that low gear ratio will be maintained in the transmission mechanism whenever and so long as the main transmission lever is in neutral or reverse, an arm (not shown) on the said spindle 19a may be linked to the shaft 43 in just the same manner as the arm 27 is linked as already described.

In the foregoing description I have referred to the oil pump as being driven by the driving shaft of the transmission mechanism, but it is to be understood that the drive is to some extent dependent upon the particular assembly of devices constituting the complete transmission. For example, a clutch may be employed located behind the gear box; a free wheel may be employed between the clutch and driving shaft or between the gear box and the back axle; and the oil pump may be driven direct from the engine.

What I claim is:

l. The combination with infinitely variable torque-responsive power transmission mechanism, of hydraulic control mechanism therefor comprising a control cylinder, a piston therein in operative association with said power transmission mechanism and under the influence of the torque reaction therefrom, a spring assisting said torque reaction, means for exerting fluid pressure on said piston to oppose said spring and torque reaction pressures, said fluid pressure means being constituted by a pump operated by the transmission mechanism and said control cylinder being provided at the fluid inlet end with a fluid leak port, and means for differentially regulating the capacity of said port from two separate sources.

2. Hydraulic control mechanism comprising a piston movable in a cylinder having a fluid inlet and a leak port adjacent said inlet, infinitely variable power transmission mechanism operatively connected to said piston, means operated by said power transmission mecham'sm to drive fluid into said cylinder, a valve or the like determining the effective capacity of the leak port, a throttle controlling the power of the prime mover of said power transmission mechanism and a valve operating element capable of actuation in conjunction with said throttle.

3. Hydraulic control mechanism comprising a piston movable in a cylinder having a fluid inlet and a leak port adjacent said inlet, infinitely variable power transmission mechanism operatively connected to said piston, means operated by said power transmission mechanism to drive fluid into said cylinder, a valve or the like determining the effective capacity of the leak port, a throttle controlling the power of the engine constituting the prime mover of said power transmission mechanism, an engine accelerator pedal, and a lost motion linkage between said valve and said pedal whereby the valve is operated only when the pedal is actuated beyond full throttle position.

l. Hydraulic control mechanism comprising a piston movable in a cylinder having a fluid inlet and a leak port adjacent said inlet, infinitely variable power transmission mechanism operatively connected to said piston, means operated by said power transmission mechanism to drive fluid into said cylinder, a valve or the like determining the effective capacity of the leak port, a throttle con trolling the power of the engine constituting the prime mover of said power transmission mechanism, an engine accelerator pedal, and a separate pedal close to said accelerator pedal, whereby the latter serves as a pivot for the foot of the operator to actuate said separate pedal when the accelerator pedal has reached the full throttle position.

5. The combination with automatically variable speed power transmission mechanism of hydraulic control mechanism therefor, the latter comprising a cylinder with an axially elongated port, a piston movable in said cylinder and connected to the transmission mechanism, means for exerting hydraulic press. c on said piston, a ported sleeve shiftable axially relatively to said cylinder, a main control lever on said transmission mechanism, and a mechanically operating connection between said main control lever and said sleeve such that whenever the lever is in neutral or reverse the said sleeve is held in the position for low gear ratio in said transmission mechanic 6. The combination with automatically variable speed power transmission mechanism of hydraulic control mechanism therefor, the latter comprising a cylinder with a valve controlled leak leading therefrom, leak adjusting mechanism for said leak valve, a piston movable in said cylinder and connected to the transmission means for exerting hydraulic pressure on said piston, a ported sleeve shiftable axially relatively to said cylinder, a main control lever on said transmission mechanism, and a mechanically operating connection between main control lever and said leak valve adjusting mechanism such that whenever the lever is in neutral or reverse the leak valve adjusting mechanism is held in the position for low gear ratio in said transmission mechanism.

7. The combination with automatically variable speed power transmission mechanism or hydraulic control mechanism therefor, the latter comprising a cylinder with a leak port at the fluid inlet end and an axially elongated port in the cylindrical wall, a settable valve controlling the capacity of said leak port, a piston movable in said cylinder and connected to the transmission mechanism, means for exertin hydraulic pressure on said piston, a ported sleeve shiftable axially relatively to said cylinder and sleeve shifting means operative in conjunction with the engine accelerator pedal of the engine or said power transmission mechanism.

8. Hydraulic control mechanism for infinitely variable speed power transmission mechanism comprising a control member for said transmission mechanism, a piston operatively connected to said control member and movable within a cylinder having a fluid inlet, a leak port of regulable efiective capacity adjacent said inlet, means for supplying pressure fluid through said inlet, a second leak port, and a sleeve movable within the cylinder to vary the effective position of said second leak port through which fluid can flow after a predetermined movement of the piston within the cylinder.

9. Hydraulic control mechanism for infinitely variable speed power transmission mechanism comprising a control member for said transmission mechanism, a piston operatively connected to said control member and movable within a cylinder having a fluid inlet, a leak port of regu-' leak port, means connecting said valve to an operating element controlling the speed of drive of said transmission mechanism, means for supplying pressure fluid through said inlet, a second leakport,anda sleeve movable within the cylinder to vary the effective position of said second leak port through which fluid can flow after a predetermined movement of the piston within the cylinder.

10. Hydraulic control mechanism comprising a piston movable in a cylinder having a fluid inlet and a leak port adjacent said inlet, infinitely variable power transmission mechanism operatively connected to said piston, means operated by said power transmission mechanism to drive fluid into said cylinder, a valve or the like determining the effective capacity of the leak port, a throttle controlling the power of the prime mover of said power transmission mechanism and means connecting said valve or the like to an operating element capable of actuation in conjunction with the throttle.

11. The combination with infinitely variable speed power transmission mechanism of hydraulic control mechanism therefor, the latter comprising a cylinder with a leak port at the fluid inlet end and an axially elongated port in the cylindrical wall, a settable valve controlling the capacity or" said leak port, a piston movable in said cylinder and connected to the transmission mechanism, means for exerting hydraulic pressure on said piston, and a ported sleeve shiftable axially relatively to said cylinder.

12. The combination with infinitely variable speed power transmission mechanism of hydraulic control mechanism therefor, the latter comprising a cylinder with a leak port at the fluid inlet end and an axially elongated port in the cylindrical wall, a piston movable in said cylinder and connected to the transmission mechanism, means for exerting hydraulic pressure substantially proportional to engine speed on said piston, and a ported sleeve shiftable axially relatively to said cylinder.

13. Hydraulic control mechanism for infinitely variable speed power transmission mechanism comprising a control member for said transmission mechanism, a cylinder having a fluid inlet and a leak port of regulable eiiective capacity adjacent said inlet, a piston operatively connected to said control member and movable in said cylinder, means for supplying pressure fluid through said inlet, a sleeve around and concentrio with said piston, a leak port in said sleeve,

said sleeve being movable within said cylinder to vary the eflective position of said sl eve leak port through which fluid can flow after a predetermined movement of the piston within the cylinder.

14. Hydraulic control mechanism for infinitely variable speed power transmission mechanism comprising a control member for said transmission mechanism, a cylinder having a fluid inlet and a leak port of regulable effective capacity adjacent said inlet, piston operatively connected to said control member and movable in said cylinder, means for supplying pressure fluid through said inlet, a leak port formed in a wall of said piston, a sleeve movable within said piston to vary the efiective position of said piston leak port through which fluid can flow after a predetermined movement of the piston within the cylinder.

JOHN LESLIE CLOUDSLEY. 

